Novel method for detecting weak magnetic fields at low frequencies

Abstract

A low-level-intensity magnetic field detection system has been designed and developed based on the amplification-selection process of signals. This configuration is also very sensitive to magnetic field changes produced by harmonic-like electrical currents transported in finite-length wires. Experimental and theoretical results of magnetic fields detection as low as 10−9T at 120Hz are also presented with an accuracy of around 13%. The assembled equipment is designed to measure an electromotive force induced in a free-magnetic-core coil in order to recover signals which are previously selected, despite the fact that their intensities are much lower than the environment electromagnetic radiation. The prototype has a signal-to-noise ratio of 60dB. This system also presents the advantage for using it as a portable unit of measurement. The concept and prototype may be applied, for example, as a nondestructive method to analyze any corrosion formation in metallic oil pipelines which are subjected to cathodic protection.

Electrostatic field of angular-dependent surface electrodes

“…If N is not large and the point of evaluation is near the contour, then it is necessary to consider many terms of the infinite sum in Eq. (24). However, if N large, we may obtain a good approximation by only taking the m = 0 term:…”

“…(26).Let us suppose that set {P n } 1≤n≤N lie on a curve whose polar equation is known R = R(φ), then λ n (r) = r 2 + R n [R n − 2(x cos γ n + y sin γ n )], Λ n (r) = y cos γ n − x sin γ n + R n sin(γ n − β n )cos γ n z sin γ n R n cos(γ n + β n ) − x cos γ n + y sin γ n with β n = 2nπ/N and R n = R(γ n ). Again, Eqs (24). and(26)can be employed to compute E E E(r) for other geometries including non-intersecting polygons.…”

“…Being only a an analogy between two different physical systems: the electrostatic where charges are static and the magnetostatic where current is time-independent.2 Generally speaking, an electric current along a wire is considered as constant. However, there are devices that emulate non-uniform distributed currents along wires (see for instance the setup in[24] which can be used in the experimental evaluation of pipe-lines' cathodic protection, the DC version of this setup would also emulate a steady non-uniform current along a wire). Another case concerns the electric current of a point-like charge moving in a loop: the electric current associated to this charge is not uniform.…”